1. Field of the Invention
This invention relates to systems and methods for measuring power characteristics of an electric circuit. More particularly, this invention relates to on-board systems and methods for measure power characteristics of a circuit or sub-circuit on a Printed Circuit Board, and for measuring temperature and thickness of the circuit or sub-circuit.
2. Description of the Related Art
Printed Circuit Boards (PCBs) are well known. PCBs are a convenient and effective way to manufacture and implement both analog and digital electronics, often referred to as integrated circuits. Today, integrated circuits on PCBs are used in a multitude of applications, such as in computers, networking equipment, electronic appliances, stereos, etc.
In general, a PCB is manufactured to design specifications and lays out the electronic circuits for the associated application, such as the wiring for an integrated circuit. Then, after the PCB has been manufactured, the elements and various components of the integrated circuit are mounted onto the PCB at touch points, such as by soldering, etc.
As integrated circuits have become more and more complex, their related power consumption and distribution becomes more demanding. Accordingly, accurate testing of an integrated circuit's power needs is essential to the production of quality integrated circuits, and in turn, electrical and electronic equipment.
Often, analytical tools such as component modeling tools or simulation tools (e.g., SPICE®, etc.) are used by design engineers to help predict power consumption and distribution across an integrated circuit. However, many factors make the accurate prediction of the characteristics of an integrated circuit unreliable. For example, it is common for a PCB to be manufactured to tolerances of up to ±10%. Similarly, component tolerances may vary. Thus, the modeling of an integrated circuit may be used for design purposes, but might not accurately predict the actual power consumption and power distribution characteristics of an integrated circuit on a PCB, which could change with the varying tolerances. Accordingly, electronics manufacturers still must rely on conventional, laboratory type testing of integrated circuits manufactured on PCBs.
The physical testing of a integrated circuit on a PCB is not without its problems. For example, it is a common practice to test an integrated circuit by “breaking up” or isolating sections of a circuit or sub-circuit on the PCB. In order to isolate a circuit or sub-circuit, a component (e.g., an inductor, etc.) is usually removed and a power source is then spliced in, such as by a wire. Then, various voltage and current measurements may be made using conventional meters (e.g., voltage and current meters, oscilloscopes, etc.). However, as electronic components become smaller, physically isolating circuits on a PCB and accurately attaching scopes and meters to the circuit becomes more cumbersome, and is often impossible.
Ideally, to perform such testing, a precision measurement of the current feeding a circuit is necessary, which can be achieved by providing a precision current source in series with the circuit, or by adding a precision resistor in series with a voltage source to a circuit. For example, referring to prior art FIG. 1, shown is a simple block diagram of a circuit 100 on a PCB. The circuit 100 has a load 102 and a voltage source 104. The power plane or PCB has a trace resistance level which is represented by R2. A precision resistor R1 is placed in series with the power plane (R2), and a precision current can be measured feeding load 102, such as by using a current meter across the precision resistor R1. However, by placing a component in series with the load (circuit) 102, the reliability of the circuit is directly related to the reliability of the precision resistor R1. Accordingly, the reliability of the entire circuit may be reduced.
Adding components in series with the circuit itself could affect the inductances of the circuit and accordingly, affect overall performance. Moreover, precision resistors also have the problem that they often cannot handle high current.
Furthermore, many circuits on a PCB are powered and connected via embedded circuits. In the example described above, the power plane is most likely embedded in the PCB, and therefore, certain characteristics of the power plane, such as thickness, will not be known. These characteristics may vary from PCB to PCB due to manufacturing tolerances. It may be important to know certain characteristics of the power plane or other embedded circuits for on-board testing of circuits or for measuring power of a circuit on a PCB.
However, since these circuits are embedded, conventional methods of measuring their thickness or other characteristics might not succeed. For example, conventional surface thickness measuring devices cannot be contacted with a power plane which is embedded in a PCB.
In view of the aforementioned problems, there is a need for new and improved systems and methods for measuring the power of a circuit on a PCB that is accurate and non-intrusive, and for measuring other characteristics of embedded circuits in a PCB. Such systems and methods should limit the number of additional components added to the circuit being tested, and should allow testers better access to circuits or less cumbersome methods to make measurements.